7,956 research outputs found
Nuclear infrared emission and the colors of IRAS galaxies
J, H, K, L', and N observations of galaxies detected at 12 microns by IRAS are combined with IRAS flux densities to investigate the relationship between the infrared sizes and colors of galaxian infrared sources. It is found that typical IRAS galaxies have 10 micron radii of 0.5 to 2.0 kpc, while active galaxies and galaxies with higher 25 to 60 micron color temperatures are smaller. One unusal object, 23060+0505, is at high redshift and has an infrared luminosity of 1.5 x 10 to the 12th power L sub 0. Its 1 to 100 micron energy distribution resembles that of a Seyfert 1 galaxy, but it shows very little sign of broad line emission in the visible. Its properties suggest that it may be a prototype for a class of highly obscured active galaxy
The TOOT Survey: status and early results
The TexOx-1000 (TOOT) radio source redshift survey is designed to find and
study typical radio-loud active galaxies to high redshift. They are typical in
the same sense that L* galaxies are typical of galaxies in the optical.
Previous surveys have only included the most luminous, rare objects at and
beyond the peak of activity at z~2, but in going a factor of 100 fainter than
the 3C survey, and in assembling a large sample, TOOT probes for the first time
the objects that dominate the radio luminosity density of the universe at high
redshift. Here we describe the current status of the TOOT survey and draw
preliminary conclusions about the redshift distribution of the radio sources.
So far, ~520 of the 1000 radio sources have redshifts, with ~440 of those in
well-defined, complete, sub-regions of the survey. For these we find a median
redshift of z=1, but the measured redshift distribution has a deficit of
objects with z~2, when compared to predictions based on extrapolating
luminosity functions constrained by higher-flux-density samples. These are the
more luminous objects that usually show emission lines, and which should not be
missed in the survey unless they are heavily reddened. The deficit may be real,
but it would not be too surprising to find a population of faint, reddened
radio sources at z~2-3 among the TOOT sources yet to have accurate redshifts.Comment: 6 pages, 2 figures. To appear in the proceedings of the conference
"Radio Galaxies: Past, present and future", Leiden, 11-15 Nov 2002, eds. M.
Jarvis et a
A New Z=0 Metagalactic Ultraviolet Background Limit
We present new integral-field spectroscopy in the outskirts of two nearby, edge-on, late-type galaxies to search for the H alpha emission that is expected from the exposure of their hydrogen gas to the metagalactic ultraviolet background (UVB). Despite the sensitivity of the VIRUS-P spectrograph on the McDonald 2.7 m telescope to low surface brightness emission and the large field of view, we do not detect H alpha to 5 sigma upper limits of 6.4 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 7321 and of 25 x 10(-19) erg s(-1) cm(-2) arcsec(-2) in UGC 1281 in each of the hundreds of independent spatial elements (fibers). We fit gas distribution models from overlapping 21 cm data of HI, extrapolate one scale length beyond the HI data, and estimate predicted H alpha surface brightness maps. We analyze three types of limits from the data with stacks formed from increasingly large spatial regions and compare to the model predictions: (1) single fibers, (2) convolution of the fiber grid with a Gaussian, circular kernel (10('') full width at half-maximum), and (3) the co-added spectra from a few hundred fibers over the brightest model regions. None of these methods produce a significant detection (>5 sigma) with the most stringent constraints on the Hi photoionization rate of Gamma(z = 0) < 1.7 x 10(-14) s(-1) in UGC 7321 and Gamma(z = 0) < 14 x 10(-14) s(-1) in UGC 1281. The UGC 7321 limit is below previous measurement limits and also below current theoretical models. Restricting the analysis to the fibers bound by the HI data leads to a comparable limit; the limit is Gamma(z = 0) < 2.3 x 10(-14) s(-1) in UGC 7321. We discuss how a low Lyman limit escape fraction in z similar to 0 redshift star-forming galaxies might explain this lower than predicted UVB strength and the prospects of deeper data to make a direct detection.U.S. Government NAG W-2166National Science FoundationUT David BrutonTexas Norman Hackerman Advanced Research Program 003658-0295-2007Cynthia and George Mitchell FoundationMcDonald Observator
Phytocannabinoids as novel therapeutic agents in CNS disorders
The Cannabis sativa herb contains over 100 phytocannabinoid (pCB) compounds and has been used for thousands of years for both recreational and medicinal purposes. In the past two decades, characterisation of the body's endogenous cannabinoid (CB) (endocannabinoid, eCB) system (ECS) has highlighted activation of central CB1 receptors by the major pCB, Δ9-tetrahydrocannabinol (Δ9-THC) as the primary mediator of the psychoactive, hyperphagic and some of the potentially therapeutic properties of ingested cannabis. Whilst Δ9-THC is the most prevalent and widely studied pCB, it is also the predominant psychotropic component of cannabis, a property that likely limits its widespread therapeutic use as an isolated agent. In this regard,
research focus has recently widened to include other pCBs including cannabidiol (CBD), cannabigerol (CBG), Δ9tetrahydrocannabivarin (Δ9-THCV) and cannabidivarin (CBDV), some of which show potential as therapeutic agents in preclinical models of CNS disease. Moreover, it is becoming evident that these non-Δ9-THC pCBs act at a wide range of pharmacological targets, not solely limited to CB receptors. Disorders that could be targeted include epilepsy, neurodegenerative diseases, affective disorders and the central modulation of feeding behaviour. Here, we review pCB effects in preclinical models of CNS disease and, where available, clinical trial data that support therapeutic effects. Such developments may soon yield the first non-Δ9-THC pCB-based medicines
The 3-D clustering of radio galaxies in the TONS survey
We present a clustering analysis of the Texas-Oxford NVSS Structure (TONS)
radio galaxy redshift survey. This complete flux-limited survey consists of 268
radio galaxies with spectroscopic redshifts in three separate regions of the
sky covering a total of 165 deg^2. By going to faint radio flux densities
(s_1.4>3 mJy) but imposing relatively bright optical limits (E R 19.5), the
TONS sample is optimised for looking at the clustering properties of low
luminosity radio galaxies in a region of moderate (0 < z < 0.5) redshifts. We
use the two point correlation function to determine the clustering strength of
the combined TONS08 and TONS12 sub-samples and find a clustering strength of
r_0(z)=8.7+/-1.6 Mpc (h=0.7). If we assume growth of structure by linear theory
and that the median redshift is 0.3, this corresponds to r_0(0)=11.0+/-2.0 Mpc
which is consistent with the clustering strength of the underlying host
galaxies (~ 2.5 Lstar ellipticals) of the TONS radio galaxy population.Comment: 18 pages, MNRAS accepted. Full paper including all spectra can be
found at http://www.noao.edu/noao/staff/brand/brand_corr_fn.ps.g
Comment on "Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics"
The incorporation of systematic uncertainties into confidence interval
calculations has been addressed recently in a paper by Conrad et al. (Physical
Review D 67 (2003) 012002). In their work, systematic uncertainities in
detector efficiencies and background flux predictions were incorporated
following the hybrid frequentist-Bayesian prescription of Cousins and Highland,
but using the likelihood ratio ordering of Feldman and Cousins in order to
produce "unified" confidence intervals. In general, the resulting intervals
behaved as one would intuitively expect, i.e. increased with increasing
uncertainties. However, it was noted that for numbers of observed events less
than or of order of the expected background, the intervals could sometimes
behave in a completely counter-intuitive fashion -- being seen to initially
decrease in the face of increasing uncertainties, but only for the case of
increasing signal efficiency uncertainty. In this comment, we show that the
problematic behaviour is due to integration over the signal efficiency
uncertainty while maximising the best fit alternative hypothesis likelihood. If
the alternative hypothesis likelihood is determined by unconditionally
maximising with respect to both the unknown signal and signal efficiency
uncertainty, the limits display the correct intuitive behaviour.Comment: Submitted to Physical Review
Methods for evaluating the performance of volume phase holographic gratings for the VIRUS spectrograph array
The Visible Integral Field Replicable Unit Spectrograph (VIRUS) is an array
of at least 150 copies of a simple, fiber-fed integral field spectrograph that
will be deployed on the Hobby-Eberly Telescope (HET) to carry out the HET Dark
Energy Experiment (HETDEX). Each spectrograph contains a volume phase
holographic grating as its dispersing element that is used in first order for
350 nm to 550 nm. We discuss the test methods used to evaluate the performance
of the prototype gratings, which have aided in modifying the fabrication
prescription for achieving the specified batch diffraction efficiency required
for HETDEX. In particular, we discuss tests in which we measure the diffraction
efficiency at the nominal grating angle of incidence in VIRUS for all orders
accessible to our test bench that are allowed by the grating equation. For
select gratings, these tests have allowed us to account for > 90% of the
incident light for wavelengths within the spectral coverage of VIRUS. The
remaining light that is unaccounted for is likely being diffracted into
reflective orders or being absorbed or scattered within the grating layer (for
bluer wavelengths especially, the latter term may dominate the others).
Finally, we discuss an apparatus that will be used to quickly verify the first
order diffraction efficiency specification for the batch of at least 150 VIRUS
production gratings.Comment: 18 pages, 11 figures. To be published in Proc. SPIE, 2012,
"Ground-Based and Airborne Instrumentation for Astronomy IV", 8446-20
- …